Add support for `nss-mdns'.

Currently, the solution is a bit hackish since running applications
will not work after a `nixos-rebuild' because `libnss_mdns' is not
in their `LD_LIBRARY_PATH'.

svn path=/nixos/trunk/; revision=11162

etc/default.nix

@@ -1,5 +1,5 @@
 { config, pkgs, upstartJobs, systemPath, wrapperDir
-, defaultShell, extraEtc, nixEnvVars, modulesTree
+, defaultShell, extraEtc, nixEnvVars, modulesTree, nssModulesPath
 }:
 
 let 
@@ -56,7 +56,9 @@ import ../helpers/make-etc.nix {
     }
 
     { # Name Service Switch configuration file.  Required by the C library.
-      source = ./nsswitch.conf;
+      source = if config.services.avahi.nssmdns
+               then (assert config.services.avahi.enable; ./nsswitch-mdns.conf)
+	       else ./nsswitch.conf;
       target = "nsswitch.conf";
     }
 
@@ -116,7 +118,7 @@ import ../helpers/make-etc.nix {
     { # Script executed when the shell starts as a login shell.
       source = pkgs.substituteAll {
         src = ./profile.sh;
-        inherit systemPath wrapperDir modulesTree;
+        inherit systemPath wrapperDir modulesTree nssModulesPath;
         inherit (pkgs) glibc;
         timeZone = config.time.timeZone;
         defaultLocale = config.i18n.defaultLocale;

etc/nsswitch-mdns.conf

@@ -0,0 +1,11 @@
+# NSS configuration files with mDNS enabled (requires running Avahi daemon).
+
+passwd:         ldap files
+group:          ldap files
+shadow:         ldap files
+
+hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4
+networks:       files dns
+
+services:       files
+protocols:      files

etc/profile.sh

@@ -1,4 +1,5 @@
 export PATH=@wrapperDir@:/var/run/current-system/sw/bin:/var/run/current-system/sw/sbin
+export LD_LIBRARY_PATH=@nssModulesPath@
 export MODULE_DIR=@modulesTree@/lib/modules
 export NIXPKGS_CONFIG=/nix/etc/config.nix
 export PAGER="less -R"

system/options.nix

@@ -986,6 +986,21 @@
         default = true;
 	description = ''Whether to allow publishing.'';
       };
+
+      nssmdns = mkOption {
+        default = false;
+	description = ''
+	  Whether to enable the mDNS NSS (Name Service Switch) plug-in.
+	  Enabling it allows applications to resolve names in the `.local'
+	  domain by transparently querying the Avahi daemon.
+
+	  Warning: Currently, enabling this option breaks DNS lookups after
+	  a `nixos-rebuild'.  This is because `/etc/nsswitch.conf' is
+	  updated to use `nss-mdns' but `libnss_mdns' is not in
+	  applications' `LD_LIBRARY_PATH'.  The next time `/etc/profile' is
+	  sourced, it will set up an appropriate `LD_LIBRARY_PATH', though.
+	'';
+      };
     };
 
     bitlbee = {

system/system.nix

@@ -125,7 +125,8 @@ rec {
 
   # NSS modules.  Hacky!
   nssModules =
-    if config.users.ldap.enable then [pkgs.nss_ldap] else [];
+       pkgs.lib.optional config.users.ldap.enable pkgs.nss_ldap
+    ++ pkgs.lib.optional config.services.avahi.nssmdns pkgs.nssmdns;
 
   nssModulesPath = pkgs.lib.concatStrings (pkgs.lib.intersperse ":" 
     (map (mod: mod + "/lib") nssModules));
@@ -175,7 +176,7 @@ rec {
   # The static parts of /etc.
   etc = import ../etc/default.nix {
     inherit config pkgs upstartJobs systemPath wrapperDir
-      defaultShell nixEnvVars modulesTree;
+      defaultShell nixEnvVars modulesTree nssModulesPath;
     extraEtc = pkgs.lib.concatLists (map (job: job.extraEtc) upstartJobs.jobs);
   };
 
@@ -255,6 +256,8 @@ rec {
   ]
   ++ pkgs.lib.optional config.security.sudo.enable pkgs.sudo
   ++ pkgs.lib.optional config.services.bitlbee.enable pkgs.bitlbee
+  ++ pkgs.lib.optional config.services.avahi.enable pkgs.avahi
+  ++ pkgs.lib.optional config.services.avahi.nssmdns pkgs.nssmdns
   ++ pkgs.lib.optional config.networking.defaultMailServer.directDelivery pkgs.ssmtp 
   ++ pkgs.lib.concatLists (map (job: job.extraPath) upstartJobs.jobs)
   ++ config.environment.extraPackages pkgs